Rare-earth Free Magnets Research Articles

HEV Motor Comparison of IPMSM With Nd Sintered Magnet and Heavy Rare-Earth Free Injection Magnet in the Same Size

In the near future, usage of heavy rare-earth element needs to be reduced, due to resource risk and rising price with vehicle electrification. This paper compared two hybrid electric vehicle traction motors of the same size using Nd sintered magnet and heavy rare-earth free magnet. We designed two interior permanent magnet synchronous motors varying only the rotor design and material. A new motor was developed using heavy rare-earth free magnet with performance and size equal to Nd sintered motor. The rotor shape was designed as the one of a synchronous reluctance motor to overcome the lack of heavy rare-earth free motor torque. The motor performance was verified with a series of experiments.

Mn2YGa (Y=Ir and Pt), a promising shape memory alloy by DFT methods

Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall Effect and rare earth free hard magnets. The Mn2Heusler compounds crystallize in the inverse cubic and tetragonal structure and are typified by antiparallel coupling of the magnetic moments on the Mn atoms. We give a comprehensive overview of the electronic and magnetic properties of both the cubic and tetragonal phases for Mn2-based Heusler materials, i.e., (Mn2IrGa and Mn2PtGa) in the ferromagnetic and antiferromagnetic ordering. Our calculation predicts that both the compounds have an inverse cubic structure in their ground states. Application of tetragonal distortion reduces the energy with respect to the cubic phase for both the materials. The equilibrium volumes of both the phases are nearly the same. The Curie temperatures and the magnetic moments of both the materials in both the cubic as well as tetragonal phases have been calculated. We find that the two materials have a high value of magnetocrystalline anisotropy for the tetragonal structure with low magnetic moments, which shows that these materials are promising candidates for spin-transfer-torque magnetization-switching applications.

Alloying with a few atomic percent of Ga makes MnAl thermodynamically stable

Ternary alloys of the form Mn55Al45-xGax have been produced in the range 0 < x < 45. In alloys with 5 < x ≤ 9 after appropriate heat treatments, two different phases with the L10 structure can be made to coexist. One is thermodynamically stable, as is binary MnGa, and the other is metastable, as is binary MnAl, but in the ternary alloys, both phases contain only a few atomic percent of Ga. The magnetic properties of the ternary alloys are superior to those of the binary analogues. The resistance to thermal decomposition of the ternary metastable phase is greatly improved compared to binary MnAl and the thermodynamically stable L10 phase does not undergo a phase transformation at temperatures up to at least 700 °C. These results enable longer processing times at higher temperatures thus facilitating the development of rare earth free MnAl-based magnets which are capable of providing a sustainable alternative to certain types of Nd-Fe-B.

Large magnetic anisotropy predicted for rare-earth-free Fe16−xCoxN2 alloys

Structures and magnetic properties of $\mathrm{F}{\mathrm{e}}_{16\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x}{\mathrm{N}}_{2}$ are studied using adaptive genetic algorithm and first-principles calculations. We show that substituting Fe with Co in $\mathrm{F}{\mathrm{e}}_{16}{\mathrm{N}}_{2}$ with a Co/Fe ratio $\ensuremath{\le}1$ can greatly improve the magnetic anisotropy of the material. The magnetocrystalline anisotropy energy from first-principles calculations reaches $3.18\phantom{\rule{4pt}{0ex}}\mathrm{MJ}/{\mathrm{m}}^{3}$ (245.6 \ensuremath{\mu}eV per metal atom) for $\mathrm{F}{\mathrm{e}}_{12}\mathrm{C}{\mathrm{o}}_{4}{\mathrm{N}}_{2}$, much larger than that of $\mathrm{F}{\mathrm{e}}_{16}{\mathrm{N}}_{2}$, and is one of the largest among the reported rare-earth-free magnets. From our systematic crystal structure searches, we show that there is a structure transition from tetragonal $\mathrm{F}{\mathrm{e}}_{16}{\mathrm{N}}_{2}$ to cubic $\mathrm{C}{\mathrm{o}}_{16}{\mathrm{N}}_{2}$ in $\mathrm{F}{\mathrm{e}}_{16\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x}{\mathrm{N}}_{2}$ as the Co concentration increases, which can be well explained by electron counting analysis. Different magnetic properties between the Fe-rich $(x\ensuremath{\le}8)$ and Co-rich $(x&gt;8)$ $\mathrm{F}{\mathrm{e}}_{16\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x}{\mathrm{N}}_{2}$ is closely related to the structural transition.

Fascinating Magnetic Energy Storage Nanomaterials: A Brief Review.

In this brief review, the importance of nanotechnology in developing novel magnetic energy storage materials is discussed. The discussion covers recent patents on permanent magnetic materials and especially covers processing of permanent magnets (rare-earth and rare-earth free magnets), importance of rare-earth permanent magnets and necessity of rare-earth free permanent magnets. Magnetic energy storage materials are those magnetic materials which exhibit very high energy product (BH)max (where B is the magnetic induction in Gauss (G) whereas H is the applied magnetic field in Oersted (Oe)). (BH)max is the direct measure of the ability of a magnetic material to store energy. In this context, processing of magnetic energy storage composite materials constituted by soft and hard magnetic materials played a predominant role in achieving high (BH)max values due to the exchange coupling phenomenon between the soft and hard magnetic phases within the composite. Magnetic energy storage composites are normally composed of rare-earth magnetic materials as well as rare-earth free magnetic materials. Nanotechnology's influence on the enhancement of energy product due to the exchange coupling phenomenon is of great prominence and therefore discussed in this review.

Metastable cobalt nitride structures with high magnetic anisotropy for rare-earth free magnets.

Metastable structures of cobalt nitrides and Fe-substituted cobalt nitrides are explored as possible candidates for rare-earth free permanent magnets. Through crystal structure searches using an adaptive genetic algorithm, new structures of ConN (n = 3…8) are found to have lower energies than those previously discovered by experiments. Some structures exhibit large magnetic anisotropy energy, reaching as high as 200 μeV per Co atom (or 2.45 MJ m-3) based on first-principles density functional calculation. Substituting a fraction of Co with Fe helps in stabilizing new structures and at the same time further improves the magnetic properties. Our theoretical predictions provide useful insights into a promising system for the discovery of new rare-earth free magnets by experiment.

Artificially produced rare-earth free cosmic magnet.

Chemically ordered hard magnetic L10-FeNi phase of higher grade than cosmic meteorites is produced artificially. Present alloy design shortens the formation time from hundreds of millions of years for natural meteorites to less than 300 hours. Electron diffraction detects four-fold 110 superlattice reflections and a high chemical order parameter (S 0.8) for the developed L10-FeNi phase. The magnetic field of more than 3.5 kOe is required for the switching of magnetization. Experimental results along with computer simulation suggest that the ordered phase is formed due to three factors related to the amorphous state: high diffusion rates of the constituent elements at lower temperatures when crystallizing, a large driving force for precipitation of the L10 phase, and the possible presence of L10 clusters. Present results can resolve mineral exhaustion issues in the development of next-generation hard magnetic materials because the alloys are free from rare-earth elements, and the technique is well suited for mass production.

ChemInform Abstract: Basics and Prospective of Magnetic Heusler Compounds

AbstractReview: 61 refs.

Do micromagnetic simulations correctly predict hard magnetic hysteresis properties?

Micromagnetic calculations using the finite element technique describe semi-quantitatively the coercivity of novel rare earth permanent magnets in dependence on grain size, grain shape, grain alignment and composition of grain boundaries and grain boundary junctions and allow the quantitative prediction of magnetic hysteretic properties of rare earth free magnets based on densely packed elongated Fe and Co nanoparticles, which depend on crystal anisotropy, aspect ratio and packing density. The nucleation of reversed domains preferentially takes place at grain boundary junctions in granular sintered and melt-spun magnets independently on the grain size. The microstructure and the nanocompostion of the intergranular regions are inhomogeneous and too complex in order to make an exact model for micromagnetic simulations and to allow a quantitative prediction. The incoherent magnetization reversal processes near the end surfaces reduce and determine the coercive field values of Co- and Fe-based nanoparticles.

Basics and prospective of magnetic Heusler compounds

Heusler compounds are a remarkable class of materials with more than 1000 members and a wide range of extraordinary multi-functionalities including halfmetallic high-temperature ferri- and ferromagnets, multi-ferroics, shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies, and magneto-caloric applications. The tunability of this class of materials is exceptional and nearly every functionality can be designed. Co2-Heusler compounds show high spin polarization in tunnel junction devices and spin-resolved photoemission. Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall effect, and rare earth free hard magnets. Most Mn2-Heusler compounds crystallize in the inverse structure and are characterized by antiparallel coupling of magnetic moments on Mn atoms; the ferrimagnetic order and the lack of inversion symmetry lead to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures, such as non-collinear magnetism, topological Hall effect, and skyrmions. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. Here, we give a comprehensive overview and a prospective on the magnetic properties of Heusler materials.

Magnetism in cubic manganese-rich Heusler compounds

Manganese-rich Heusler compounds are attracting much interest in the context of spin transfer torque and rare-earth free hard magnets. Here we give a comprehensive overview of the magnetic properties of non-centrosymmetric cubic Mn$_2$-based Heusler materials, which are characterized by an antiparallel coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures. In terms of the band structure calculations, we explain the formation of this magnetic order and the Curie temperatures. This overview is intended to establish guidelines for a basic understanding of magnetism in Mn2 -based Heusler compounds.

Kinetics of tetrataenite disordering

Tetrataenite is a chemically ordered L10-type Fe50Ni50 alloy detected for the first time in 1977 by 57Fe Mössbauer spectroscopy studies in iron meteorites. The thermal history of meteorites, in particular short thermal events like those associated to hypervelocity impacts, can be constrained by tracing the presence of tetrataenite or its disordering into taenite. The knowledge of the disordering kinetics of tetrataenite, that is associated with changes in its magnetic properties, is still very fragmentary so that the time–temperature history of these meteorites cannot be constrained in details. Furthermore, knowledge of disordering kinetics is important due to potential technological application of tetrataenite as a rare-earth free strong magnet. Thus, this work provides the first time–temperature data for disordering reaction of tetrataenite. We have shown that disordering is not an instantaneous process but is a kinetic limited reaction. It was shown that disordering may take place at any temperature above the order–disorder transition for L10 superstructure phase (~320 °C) when the appropriate time-scale is considered. This result means that the apparent Curie point for tetrataenite is not an absolute property in the sense that any estimate of this parameter should be referred to a given time-scale.

Low-temperature phase MnBi compound: A potential candidate for rare-earth free permanent magnets

The low-temperature phase (LTP) MnBi is one of the few rare-earth free compounds that exhibit a large magnetocrystalline anisotropy energy in the order of 106J/m3. A large coercive field (μ0Hcj) above 1T can be obtained readily by reducing the crystallite size (D) through mechanical grinding (MG). The room-temperature Hcj values follow a phenomenological expression μ0Hcj=μ0Ha(δ/D)n where the anisotropy field (μ0Ha) is ∼4T, the Bloch wall width (δ) is 7nm and the exponent (n) is about 0.7 in our study. The grain refinement upon MG is accompanied by suppression of the spin reorientation transition temperature (TSR) from 110K to below 50K. The coercive field starts to exhibit positive temperature dependence approximately 50K above TSR and the room-temperature magnetic hardening induced by MG could partially be brought about by the lowered onset of this positive temperature dependence. The suppression of TSR by MG is likely to be induced by the surface anisotropy with which the 2nd order crystal field term is enhanced. One of the shortcomings of LTP-MnBi is its poor phase stability under the ambient atmosphere. The spontaneous magnetization decreases considerably after room-temperature aging for 1week. This is due to oxidation of Mn which leads to decomposition of the MnBi phase. Hence, the surface passivity needs to be established before this material is considered for a permanent magnet in practical uses. Another shortcoming is the limited spontaneous magnetization. The theoretical upper limit of the maximum energy product in LTP-MnBi remains only a quarter of that in Nd2Fe14B. Nevertheless, owing to the unique positive temperature dependence of the first-order anisotropy constant (K1), the hardness parameter (κ) of LTP-MnBi is enhanced above room temperature; κ reaches as large as 2.8 at 580K. This makes LTP-MnBi a possible candidate for the hard phase in rare-earth free nanocomposite magnets.

희토류 대체 영구자석의 연구동향: 교환 스프링자석

영구자석은 산업전반에 광범위 하게 쓰이고 있는 핵심 부품중의 하나이다. 이러한 영구자석을 만드는데 필수적으로 이용되고 있는 원소가 바로 희토류 계열의 원소들이다. 이미 널리 알려져 있는 것처럼 희토류 생산의 대부분은 중국이 차지하고 있고, 이러한 원인에 의해 전 세계적으로 희토류 원소의 생산 및 공급 불균형에 의해 발생하는 많은 문제점들을 인식하고 있다. 이를 해결하기 위해 희토류 기반 영구자석을 대체하기 위한 다양한 방안들이 논의 되고 있으나 현재까지 명확하게 희토류 대체 영구자석이 가능한 물질 혹은 구조에 대한 제시는 없다. 본 논문에서는 여러 가지 가능성 중에 교환스프링 자석구조에 대해서 논의하고자 한다. Permanent magnet is one of the most important parts in modern industry and the rare earth elements play an essential role for operation of permanent magnet. As is well known, the rare earth elements are mostly produced in China and the world is now facing serious problems owing to supply and demand imbalances. Many attempts have been performed to replace these rare-earth based permanent magnets by rare-earth free magnets, but they have not been successful so far. Regarding this issue, we discuss about an exchange spring magnet as a potential rare earth free permanent magnet structure.

Rare earth free exchange spring magnet FeCo/FePt(001): Giant magnetic anisotropy and energy product

Using the full potential linearized augmented plane wave (FLAPW) method, we have investigated the thickness dependent magnetic properties of rare earth free exchange spring magnet FeCo/FePt(001). The FeCo adlayer thickness is increased from one monolayer (ML) to four ML coverage. It is observed that the FeCo adlayers and Fe atoms in FePt substrate show almost half metallic behavior, while an ordinary metallic feature is found in Pt atoms. The average magnetization increases with FeCo thickness and the estimated maximum energy product reaches 66MGOe in FeCo(4ML)/FePt(001). A giant perpendicular magnetocrystalline anisotropy (MCA) energy of 18.20meV/cell is found in pure FePt(001) and it becomes 17.35meV/cell even in FeCo(4ML)/FePt(001). In addition, we find very large coercivity field in FeCo/FePt(001) systems. For instance, the calculated maximum coercivity field in FeCo(4ML)/FePt(001) is about 188kOe. Both energy product and coercivity field calculations may imply that the FeCo/FePt can be utilized for potential rare earth free exchange spring magnet material.

Hard Magnetic Materials: A Perspective

The principles of operation of permanent magnets are summarized, and their development is reviewed. The key figure of merit, the energy product, improved exponentially over much of the 20th century, doubling roughly every 12 years. Yet it has not improved significantly in the last 20 years. Constraints on further development are explained, together with the limits of 1/4 μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on energy product and 2K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> on coercivity, where K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> is the uniaxial anisotropy constant and Ms is the spontaneous magnetization. The challenge of making rare-earth free magnets with a large energy product is discussed, as well as nanocomposite megajoule magnets and the development of new magnetically hard thin-films with perpendicular anisotropy which are potentially interesting for spin electronics or magnetic recording.